Web cooling device for a vacuum processing system

ABSTRACT

Described are a device and a method for cooling a web in a vacuum processing system. The device includes a heat transfer module, a coolant path and a gas injector. The heat transfer module has a first end, a second end opposite the first end, and a pair of cooling surfaces extending between the first and second ends. The first end receives a transported web in a vacuum environment and the second provides the transported web after passage through a web transport path between the cooling surfaces. The coolant path is in thermal communication with the heat transfer module to maintain the cooling surfaces at a temperature less than the temperature of the transported web. The gas injector supplies gas to the web transport path between the cooling surfaces so that heat is efficiently conducted from the transported web to the cooling surfaces.

FIELD OF THE INVENTION

The invention relates generally to a device and method for cooling a web in a web vacuum processing system such as a vacuum deposition system. More particularly, the invention relates to a device that cools a web by flowing gas through a web transport path inside a heat exchanger.

BACKGROUND

Roll to roll thin film vacuum deposition is often used to coat flexible materials such as plastics, metals and polyimide. In typical configurations a material such as a web substrate or tape is unwound from a payout roll into a processing chamber. After a series of steps are performed, the coated web substrate is wound onto a take-up roll. Many of the deposition technologies that are commonly used require high vacuum conditions, for example, a pressure less than 1 Torr. High vacuum deposition technologies include vacuum evaporation and sputtering, often referred to generically as physical vapor deposition. The deposition process induces a heat load on the web, resulting in an increase in temperature. A variety of sources may generate the heat load. For example, the heat load can be due to the heat of condensation of the growing film, a hot surface of the process apparatus that is in the line of sight of the web substrate, and ion or electron currents due to proximity to a plasma during sputtering. In many applications, the increase in the temperature of the web is unacceptable. For example, at high coating speeds and web transport rates, the heat load can cause the web to wrinkle and crease, possibly resulting in permanent damage to the web. As the heat load is typically proportional to the deposition rate, the throughput of the deposition system is severely limited. Consequently, a means to cool the web during deposition can be used to increase the throughput and productivity of the deposition system.

A rotating cooling drum can be used to cool the web during the deposition process. The thermal conductance between the web and the cooling drum affects the ability to control the temperature rise of the web during the coating process, and sets an upper limit to the coating speed. The cooling drum can be used to introduce a gas between the drum surface and the web to increase the rate of heat transfer; however, gas may be introduced in the vacuum region of the system and adversely affect the deposition process.

SUMMARY

In one aspect, the invention features a device for cooling a web. The device includes a heat transfer module, a coolant path and a gas injector. The heat transfer module has a first end, a second end opposite the first end, and a pair of cooling surfaces extending between the first and second ends. The first end has an entrance aperture to receive a transported web in a vacuum environment and the second end has an exit aperture to provide the transported web after passage through a web transport path between the cooling surfaces. The coolant path is in thermal communication with the heat transfer module to remove heat from the module. The gas injector is configured to inject a gas into the web transport path between the cooling surfaces so that heat is conducted from the transported web to the cooling surfaces.

In another aspect, the invention features a method for cooling a web in a vacuum processing environment. A pair of cooling surfaces is maintained at a temperature that is less that a temperature of a web in the vacuum processing environment. The web is transported along a path between the cooling surfaces and a gas flows along at least a portion of the path between the cooling surfaces. Heat is conducted from the web through the gas to the cooling surfaces so that the temperature of the web is reduced.

In yet another aspect, the invention features a web heat transfer device. The device includes a heat transfer module, a heat transfer fluid path and a gas injector. The heat transfer module has a first end, a second end opposite the first end, and a pair of heat transfer surfaces extending between the first and second ends. The first end has an entrance aperture to receive a transported web in a vacuum environment and the second end has an exit aperture to provide the transported web after passage through a web transport path between the heat transfer surfaces. The heat transfer fluid path is in thermal communication with the heat transfer module to maintain the heat transfer surfaces at a temperature that is different from a temperature of the transported web. The gas injector is configured to inject a gas into the web transport path between the heat transfer surfaces to thereby conduct heat between the heat transfer surfaces and the transported web.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further advantages of this invention may be better understood by referring to the following description in conjunction with the accompanying drawings, in which like numerals indicate like structural elements and features in the various figures. For clarity, not every element may be labeled in every figure. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

FIG. 1 illustrates an embodiment of a web cooling device according to the invention.

FIG. 2A is a cross-sectional view of the web cooling device of FIG. 1.

FIG. 2B is an orthogonal cross-sectional view of the web cooling device of FIG. 1.

FIG. 2C is a cross-sectional view of a single rod and gasket feature for the web cooling device of FIG. 2A.

FIG. 3 is a view of the inside surface of the upper plate of the web cooling device of FIG. 1.

FIG. 4 is a view of the inside surface of a bottom plate of another embodiment of a web cooling device according to the invention.

FIG. 5 is a cross-sectional view of the embodiment of a web cooling device according to FIG. 4.

FIG. 6 is a simplified orthogonal cross-sectional depiction of the web cooling device of FIG. 5.

FIG. 7 is a simplified cross-sectional depiction of another embodiment of a web cooling device according to the invention.

FIG. 8 is a graph showing the end temperature of a transported web as a function of the gas flow rate and showing the heat transfer coefficient as a function of the gas flow rate achieved with an embodiment of a web cooling device in accordance with the invention.

DETAILED DESCRIPTION

A common technique for cooling a web in a vacuum environment is to transport the web over a cooled roll or drum so that heat is transferred to the drum through contact. Cooling is adjusted by varying the temperature of the roll and the wrap angle of the web around the roll. The cooling rate is proportional to h*(T₀−T) where h is the heat transfer coefficient, T₀ is the temperature of the cooling roll and T is the temperature of the web. In vacuum, the interface between two materials generally does not have a high heat transfer coefficient h. More specifically, the natural roughness of a material at a microscopic level results in sharp points of contact; however, as heat conduction is proportional to the cross-sectional contact area, the transfer of heat across the interface is substantially limited. The introduction of a gas or a pliable material, such as an elastomer, between the materials results in a substantial improvement in cooling efficiency. The pliable material increases the effective area of contact while the gas provides a heat conduction path between the materials.

In many applications, the pressure for sufficient gas conduction is in a range from less than 10 Torr to more than 20 Torr. To sustain this pressure, a force is applied between the web and the cooling device, and gas is injected into the micro-spaces between the two surfaces. This gas injection technique has been applied to achieve cooling of semiconductor wafers using a cooling chuck. Multiple gas injectors are used to achieve a uniform pressure between the wafer and the chuck. The resulting gas load to the vacuum chamber is generally low and does not interfere with the deposition process.

In web coating applications, the web is continuously transported on a rotating roll so that trapping a gas between the web and the roll is more complicated than the technique used with semiconductor wafer coating applications. Multiple gas injectors can be provided around the circumference of the roll. During operation, the roll is continuously rotating and the wrap angle for most applications typically limits the contact between the web and the surface of the roll. In some implementations, the injectors introduce gas directly into the chamber, thereby increasing the load to the vacuum system while not contributing to the cooling of the web. U.S. Patent Application Publication No. US 2012/0006520 discloses an apparatus for cooling a web that introduces gas in the region where the web is in contact with a roll; however, the size and efficiency is not adequate for some web coating applications.

Embodiments of a web cooling device according to the present invention provide for a high heat transfer coefficient h between a web and the device while limiting the volume of gas introduced into the vacuum deposition chamber during a process run. Advantageously, the device enables higher deposition rates and increased productivity. In general, the device includes a heat transfer module having a pair of cooling surfaces extending between opposite ends of the module. A web transported through a vacuum environment enters one end of the module through an entrance aperture and exits the opposite end of the module at an exit aperture. A coolant path is in thermal communication with the module to maintain the cooling surfaces at a temperature substantially less than the temperature of the web. A gas injector introduces a flow of gas between the cooling surfaces and the surfaces of the web. The gas provides a thermally conductive path to remove heat from the web. Some embodiments of the device do not include moving parts while other embodiments employ a small number of rollers that come into contact with one or both surfaces of the web and help to accurately define a transport path through the device. The complexity and cost for manufacturing the device are low in comparison to various types of cooling drums while cooling efficiency and reliability during operation are increased.

The device can be used with a variety of web substrates and coating materials. By way of a non-limiting example, the web can be a stainless foil substrate having a thickness in a range of approximately 25 μm to 100 μm. Other substrate thicknesses and other substrate materials, such as polyimide, aluminum, titanium and copper, can be used. Examples of materials that can be deposited on the web substrate include molybdenum, chromium, titanium and oxides, such as silicon dioxide and zinc oxide. Film thicknesses typically are in a range of approximately 50 nm to 1 μm, although other thicknesses can be used.

FIG. 1 illustrates an embodiment of a web cooling device 10 according to principles of the invention. The device 10 functions as a heat transfer module that can cool a web 12 (or tape) processed in vacuum, for example, in a vacuum deposition system. The device 10 includes a pair of plates 14A, 14B, top and bottom coolant paths 16A, 16B, a gas injector port 18 and a vacuum port 20. The plates 14 are secured to each other using bolts 22 or other fasteners to maintain the plates in a parallel configuration. The plates 12 are fabricated from a thermally conductive material such as aluminum or other metal.

The gas injector port 18 is configured for coupling to tubing or other form of conduit to receive a flow of gas from a gas source. For example, the gas injector port 18 can be coupled to an argon source. Other coolant gases such as hydrogen, helium, nitrogen or oxygen can be used.

The top coolant path 16A is in the form of a tube that resides in a channel in the top plate 14A. For example, the tube may be a copper tube or aluminum tube. The second (bottom) coolant path 16B is a tube that is disposed in a similarly shaped channel on the opposing plate 14B. Each coolant path 16 conducts a coolant from an entrance port 24A to an exit port 24B. In one embodiment, the coolant is chilled water that is provided to the entrance port 24A from a water chiller through tubing and returned to the water chiller through tubing coupled to the exit port 24B. In other embodiments, other numbers of coolant paths can be used and the shape of the coolant paths can be different.

Reference is also made to FIG. 2A which is a cross-sectional view of the web cooling device 10 through the gas injector port 18 and vacuum port 20, and FIG. 2B which is an orthogonal cross-sectional view of the device 10 through the gas injector port 18. Portions of a vacuum plenum 26 are visible near the web entrance and exit apertures 28A and 28B, respectively, for a web transported from left to right in FIG. 2A. A linear gasket 29 is provided along each side of the device 10. The device 10 also includes gas conductance limiters disposed along the web transport path. The gas conductance limiters in the illustrated embodiment include eight pairs of rod and gasket features 30 that reduce the gas load on the vacuum system. In preferred embodiments, the gas pressure in the center of the device 10 between the innermost gas conductance limiters is maintained at a pressure in a range of 0.5 Torr to 20 Torr.

A cross-sectional view of a single rod and gasket feature 30 is shown in FIG. 2C and includes a linear channel 32 that extends lengthwise along the surface of the plate 14 (i.e., into the page of the illustration) and perpendicular to the gas flow. A small diameter (e.g., 0.125 in.) TEFLON® rod 34 is disposed in the channel 32 and is urged outward towards the web transport path by a linear gasket 36 of resilient material that is disposed in a narrow groove 38.

FIG. 3 shows the inside surface of the upper plate 14A which acts as a cooling surface. The inside surface includes a recessed region 40 (i.e., channel) in the shape of a “backwards C.” The inside surface of the lower plate 14B also acts as a cooling surface and has a similar configuration, including a similarly shaped recessed region. In the fully assembled web cooling device 10, the recessed regions 40 in each plate 14 oppose each other and form the vacuum plenum 26. The single channel vacuum plenum 26 extends to both ends of the device 10 and allows for pumping through the single vacuum port 20. The upper plate 14A also includes a gas inlet 42 in communication with the gas injector port 18 and a vacuum opening 44 in communication with the vacuum port 20.

Operation is described here with reference to FIG. 1 and FIG. 2. Gas injected between the plates 14 flows toward the entrance and exit apertures 28 due to the pressure differential between the gas injector port 18 and the ends of the vacuum plenum 26 near the entrance and exit apertures 28. The linear gaskets 29 prevent gas from escaping out through the sides of the device 10. Each rod 30 is pushed towards its opposing rod 30 so that the web 12 is guided between the pairs of rods 30 and along the web transport path through the device 10. The pairs of rods 30 also limit the gas flow through along the web transport path.

In a preferred embodiment, the web cooling device has a configuration similar to that described above for the device 10 of FIG. 1; however, instead of Teflon® rods, pairs of opposing rollers are used to guide the web and limit gas conductance. In this embodiment, the bottom plate 50B of the device includes four stainless steel rollers 52 as shown in FIG. 4. The rollers 52 are disposed in channels 54 and are attached at each end to bearings that allow each roller 52 to freely rotate about its cylindrical axis. The bottom plate 50B is shown sandwiched between two side members 50D although in alternative embodiments the bottom plate 50B and side members 50D can be of unitary construction.

FIG. 5 shows a cross-sectional view of the web cooling device 62 through one of the pairs of rollers 52 closest to the middle of the device 62. Each roller 52 terminates at each end in a bearing 56 in the respective side member 50. In addition, each roller 52 radially protrudes a small distance out from its channel 54 into the gap between the inner surfaces of the plates 50. The separation between opposing rollers 52 is less than the plate separation and greater than the thickness of the web. By way of a non-limiting example for a 0.004 in. thick web, the separation between opposing rollers may be between 0.010 in. and 0.020 in. and the separation between the plates 50 may be 0.040 in. to 0.080 in. The roller separation limits the gas conductance along the web transport path while assisting in guiding the web through the device without touching the plates 50. Linear seal segments 60 are disposed in dove-tailed grooves in the upper side members 50C to reduce or prevent gas from escaping from the interface of the side members 50C, 50D along the sides of the device 62.

FIG. 6 is a simplified orthogonal cross-sectional depiction of the web cooling device 62 of FIG. 5. The pairs of rollers 52 guide the web 12 as it is transported through the device 62. Gas flow is limited to the volume between the inner surfaces of the plates 50 that is not occupied by the web 12. Moreover, as gas flows from the gas inlet 40 to the left and to the right in the web transport path, the gas flow is increasingly restricted at each pair of opposing rollers.

FIG. 7 shows a simplified cross-sectional depiction of an alternative configuration for an assembled web cooling device 70. Only one of the plates 72B has channels occupied by rollers 52. In this embodiment, the separation between the inner surfaces of the plates 72 can be substantially less than the separation between the inner surfaces of the plates 50 for the device 62 of FIG. 6 because the web 12 is guided through continuous contact with rollers 52 on a single side of the web transport path. This embodiment utilizes a change in the direction of the web transport path at the entry and at the exit apertures 74 of the device 70 to ensure contact with the rollers 52. In particular, the direction of transport changes at the first roller 52A and again at the last roller 52D. Only one side of the web 12 is in contact with the rollers 52, therefore this embodiment is preferable in applications where one side of the web 12 cannot be disturbed during passage through the device 70.

In the various embodiments of a web cooling device described above, an increase in the gas flow rate through the device results in improved cooling of the web. For example, FIG. 8 is a graph showing the end temperature of the web at the exit aperture 28B (FIG. 2) as a function of the gas flow rate in standard cubic centimeters per minute. FIG. 8 also shows how the heat transfer coefficient h varies as a function of the gas flow rate. The graphed functions are based on measurement data obtained at three different gas flow rates.

Embodiments of the devices described above are primarily related to web cooling applications for vacuum deposition systems; however, it should be recognized that the device can be used to cool a web in combination with any process that heats the web in a vacuum environment. For example, the device can be used in conjunction with a plasma cleaning application. Moreover, the device can be configured more generally as a web heat transfer device wherein the coolant path is instead a heat transfer fluid or gas path, and the cooling surfaces are heat transfer surfaces. Thus in some embodiments the device supplies a heated fluid or gas to maintain the heat transfer surfaces at a temperature that is greater than the transported web. As a result, the temperature of the web is increased by heat conducted from the heat transfer surfaces to the web.

While the invention has been shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as recited in the accompanying claims. 

What is claimed is:
 1. A web cooling device, comprising: a heat transfer module having a first end, a second end opposite the first end, and a pair of cooling surfaces extending between the first and second ends, the first end having an entrance aperture to receive a transported web in a vacuum environment and the second end having an exit aperture to provide the transported web after passage through a web transport path between the cooling surfaces; a coolant path in thermal communication with the heat transfer module to remove heat therefrom; and a gas injector configured to inject a gas into the web transport path between the cooling surfaces to thereby conduct heat from the transported web to the cooling surfaces.
 2. The web cooling device of claim 1 wherein the heat transfer module comprises a pair of parallel plates each having one of the cooling surfaces.
 3. The web cooling device of claim 1 wherein the heat transfer module has at least one plenum in communication with the region between the cooling surfaces and proximate to at least one of the entrance aperture and the exit aperture, the at least one plenum configured for coupling to a vacuum pump to thereby establish a flow of the gas from the gas injector to the plenum along at least a portion of the web transport path.
 4. The web cooling device of claim 1 further comprising a first plurality of rollers each disposed in a channel in one of the cooling surfaces along a side of the web transport path and a second plurality of rollers each disposed in a channel in the other of the cooling surfaces along an opposite side of the web transport path, each of the rollers extending radially into the web transport path, each roller in the first plurality of rollers being opposite a respective one of the rollers in the second plurality of rollers, wherein the transported web is guided between the two rollers in each of the pairs of rollers and wherein each of the pairs of rollers limits a gas conductance through the web transport path.
 5. The web cooling device of claim 1 further comprising a plurality of gas conductance limiters disposed along the web transport path.
 6. The web cooling device of claim 1 further comprising a plurality of rollers each disposed in a channel in one of the cooling surfaces along a side of the web transport path, each of the rollers extending radially into the web transport path, wherein only one side of the transported web is in contact with the rollers and wherein the rollers limit a gas conductance through the web transport path.
 7. The web cooling device of claim 6 wherein a direction of transport for the transported web changes at a first one of the rollers and a last one of the rollers.
 8. The web cooling device of claim 1 wherein a separation between the cooling surfaces does not exceed 0.080 inches.
 9. The web cooling device of claim 1 further comprising a source of gas in communication with the gas injector.
 10. The web cooling device of claim 9 wherein the gas comprises a gas selected from a group of gases consisting of hydrogen, helium, nitrogen, oxygen and argon.
 11. The web cooling device of claim 1 further comprising a plurality of rods each disposed in a channel in one of the cooling surfaces along a side of the web transport path, each of the rods extending radially into the web transport path, wherein the transported web is guided between the rods and the other of the cooling surfaces and wherein the rods limit a gas conductance through the web transport path.
 12. A method for cooling a web in a vacuum processing environment, the method comprising: maintaining a pair of cooling surfaces at a temperature less that a temperature of a web in a vacuum processing environment; transporting the web along a path between the cooling surfaces; and flowing a gas along at least a portion of the path between the cooling surfaces, wherein heat is conducted from the web through the gas to the cooling surfaces to thereby reduce the temperature of the web.
 13. The method of claim 12 wherein the cooling surfaces are parallel to each other.
 14. The method of claim 12 wherein maintaining the pair of cooling surfaces at a temperature less that a temperature of the transported web comprises flowing a coolant through a coolant path that is in thermal communication with the cooling surfaces.
 15. A web heat transfer device, comprising: a heat transfer module having a first end, a second end opposite the first end, and a pair of heat transfer surfaces extending between the first and second ends, the first end having an entrance aperture to receive a transported web in a vacuum environment and the second end having an exit aperture to provide the transported web after passage through a web transport path between the heat transfer surfaces; a heat transfer fluid path in thermal communication with the heat transfer module to maintain the heat transfer surfaces at a temperature that is different from a temperature of the transported web; and a gas injector configured to inject a gas into the web transport path between the heat transfer surfaces to thereby conduct heat between the heat transfer surfaces and the transported web. 